Technology in the areas of telecommunications and computer systems is continually challenged to provide increased processing speeds with lower power requirements. Lap top computer systems provide a particular challenge in this respect in that higher processing speeds and lower power requirements form the basis for a competitive advantage for a supplier. Users of personal computer systems, especially lap top computer users, are also demanding increased functionality in addition to the enhanced speed and power requirements. One such demand is the ability to reliably connect to a telephone line to transmit and receive data at high data speeds. For example, since the wide use of the Internet, consumers are demanding that modems connect at the same high data speed each time they connect to the Internet.
Personal computer systems use very fast internal clock signals, which are approaching the realm of one gigahertz, to achieve the fast processing rates. The fast clock signals generate considerable electrical noise that is picked up by the various interconnections inside the computer system. The electrical noise typically manifests itself as a common mode signal which can occur on the signal return or "ground" lines causing the lines to "bounce." If the interfering signals become too large or their effect is not properly accounted for, the interfering signals can cause the operation of the computer system to become intermittent or unreliable. One approach to minimizing the effect of the common mode signals is the use of differential input signals.
A differential input signal consists of two signals wherein the information to be presented is supplied as the signal inverses (i.e., 180 degrees out of phase) or logical complements of each other. A common mode noise signal would add equally to each of the interconnecting lines or traces carrying a differential input signal if the two lines are in close proximity to one another. As long as a circuit can determine the differential input signal, even in the presence of a large common mode noise signal, the circuit will reliably respond to the logic command intended thereby overcoming the common mode noise interference.
A commonly used differential input circuit in computer and telecommunication systems is a comparator circuit. When used in concert with other logic elements having single-ended logic inputs, the differential input comparator accepts a differential input signal and converts the differential logical information to a single-ended logic output signal. The comparators form critical circuit elements in modern computer and telecommunications systems and are, therefore, subject to the same requirements of increased processing speed with lower power usage.
Accordingly, what is needed in the art is a differential comparator that demonstrates satisfactory throughput capability while minimizing the impact on power requirements.